The present invention generally relates to vacuum bag molding and, more particularly, to curing resins using the vacuum bag molding process.
Referring to FIGS. 1 and 2, one method of vacuum-bag molding may comprise placing an uncured object such as a wing panel 12 or tail panel into a substantially gas-impermeable container or bag 18 and removing air or a gas, from the gas-impermeable bag 18 with a pump (not shown). A breather material 20 and a release film 22 may be applied between the gas-impermeable bag 18 and the wing panel 12 to prevent the gas-impermeable bag 18 from adhering to the wing panel 12 while the wing panel is curing. The gas-impermeable bag 18 and wing panel 12 are then placed on a lay-up mandrel 32 and cure in an auto-clave. The auto-clave may apply pressure and heat to consolidate layers of the curing wing panel 12 so as to remove entrapped air and volatiles, and to cure the wing panel 12. The gas-impermeable bag 18 generally has a skin tight fit to the wing panel 12, and thus translates the auto-clave pressure to the wing panel 12 such that there are relatively no undesired undulations of the wing layers.
However, as best shown in FIG. 2, there may be a low-pressure volume 28 interacting with the surface 34 of the curing wing panel 12, where the pressure is lower than the ambient pressure produced by the auto-clave. This lower pressure volume 28 may cause an undulation 30 in a wing layer. A cause for the low pressure volume is the bridging 26 of the gas-impermeable bag 18 over the base 24 of the stringer 10 to the curing wing panel 12, such that the auto-clave pressure does not translate to the curing wing panel 12. This problem may occur, but is not limited to, where one or more curing objects have a geometry that causes bridging. Undulations in a layer of a composite object reduce the tensile strength of an object. Undulations also increase production time and costs, as specially prepared shims may be required to mate parts to the object with undulations; for example mating a rib to a wing panel.
Also, it may be desirable when two objects are joined, that each object be uncured. Curing an object within an auto-clave may be an expensive and time consuming process as the auto-clave is typically reheated and repressurized during each curing cycle. Joining and curing two uncured objects together would eliminate one auto-clave cycle by combing two separate cycles into one. However, each object may be composed of a different resin and if each object is uncured, the resins of each object may mix, causing undesired properties.
As can be seen, there is a need for applying a pressure to all surfaces of an object while it is curing. Also, there is a need for coupling two or more curing objects such that there is no mixing of dissimilar resins. Moreover, there is a need for producing a part that has a predictable geometry so that the part may be joined to other parts without shimming.